em 
ADVERTISEMENT. 
Tux present work is published by the SMITHSONIAN INSTITUTION in Co- 
operation with the Museum oF ComPARATIVE ZooLocy, Cambridge, Mass., 
the drawings for the plates having been made at the expense of that estab- 
lishment. 
This work has been recommended by Mr. ALEXANDER AGASSIZ. 
In accordance with the rule of the Institution, requiring the formal approval 
by selected experts of every Memoir offered for publication in the Smithsonian 
“ Contributions to Knowledge,” it was submitted for examination to CHARLES 
A. Wurrr and to Wititiam H. Dati; by whom it was also strongly com- 
mended, and it has been accordingly accepted for publication in the series of 
“ Contributions.” 
S. P. LANGLEY, 
Secretary Smithsonian Institution. 
SMITHSONIAN INSTITUTION, 
Wasuineton, D. C., February, 1889. 
